1. Field of the Invention
The present invention relates to a device for determining periodic power consumption of an electrically operated appliance and more particularly relates to a device and method for activating an electric component of the electrically operated appliance in response to the determined periodic power consumption of the electrically operated appliance.
2. Description of the Related Art
A refrigerator typically is provided with a defrosting control system for removing frost which has accumulated on the evaporator coils of a refrigerator during a cooling cycle. A typical defrosting control system is illustrated in FIG. 1 and generally includes a motor driven switch timer (10) which effectively counts the cumulative running time of a compressor (12) so as determine when the cooling cycle is to be terminated so as to initiate a defrosting cycle. The refrigerator circuit, including the motor driven switch timer (10), is activated when a freezer temperature control switch (16) closes, caused generally by the refrigerator having a storage compartment temperature above a prescribed value. When switch (16) opens, the refrigerator is in effect off. A defrost heater (14) is provided for thawing the frost accumulated on the evaporator coils (not shown) along with a defrost terminator (18) for detecting the temperature of the evaporator coils so as to disable the energization of the defrost heater (14).
The defrosting operation is controlled and carried out periodically by the motor driven switch timer (10) which is typically detachably coupled to the control circuitry of the refrigerator at quick-connect terminals to facilitate replacement if necessary. The duty cycle of refrigeration to defrost is fixed by the refrigerator manufacturer and implemented in the motor driven switch timer (10), with generally six hours of cooling to thirty minutes of defrosting. There are no adjustments to compensate for variations in the operating environment, and as such the same ratio is used in a refrigerator disposed in Alaska as compared to a refrigerator used in Florida.
In operation, when the freezer temperature control switch (16) closes, the cooling compressor (12) is activated, and the cumulative running time of compressor (12) is counted by the motor driven switch timer (10). After the compressor (12) has been energized for a prescribed period of time, such as, e.g., six hours, the motor driven switch timer (10) immediately de-energizes the compressor (12) and consequently energizes the defrost heater (14) through the provision of an internal switch (10a). The motor driven switch timer (10) thereafter enables the defrost heater (14) to be energized when the defrost terminator (18) is in a closed position. Typically, the defrost terminator (18) will be in a closed position when the temperature of the evaporator coils are below a prescribed value (e.g., 20.degree. F.). In particular, the motor driven switch timer (10) enables the defrost heater (14) to be energized only during a defrosting duty cycle which is typically a thirty minute period which is prescribed by the motor driven switch timer (10). While the defrost heater (14) is energized, any frost on the evaporator coils are gradually thawed by radiant heat from the defrost heater (14). The accumulation of ice and frost on the evaporator coils restricts the coils from drawing heat out of the food compartment since the ice acts as an insulator, thus lowering the efficiency of the coils, and consequently, the refrigerator. In accordance with the energization of the defrost heater (14), the temperature of the evaporator coils gradually rises. In this time period, (such as, e.g., a half hour) the defrost terminator (18) detects the temperature of the evaporator coils. When the temperature of the evaporator coils reaches a prescribed value, (such as, e.g., 50.degree. F.) the defrost terminator moves to an open position and the defrost heater (14) is deenergized, whereafter the compressor (12) is returned to an operational state by the motor driven switch timer (10) after the half hour duty cycle of the defrost heater (14) has expired.
In typical refrigerator control systems, such as illustrated in FIG. 1, the motor driven switch timer (10) only operates when the refrigerator's settable freezer temperature control switch (16) is closed (usually when the temperature in the storage compartment of the refrigerator is above a prescribed temperature, e.g., 50.degree.). As illustrated in FIG. 2, a defrost cycle must always interrupt and supersede a cooling cycle. Further, the cooling cycle may not be resumed, (regardless of the position of the defrost terminator (18), until after the defrost duty cycle, as prescribed in the motor driven switch (10), has expired. FIG. 2 illustrates a refrigerator energy consumption graph including a defrost cycle consisting of thirty minutes which comprises regions (2) and (3). Only after expiration of the defrost duty cycle, may the motor driven switch timer (10) initiate a cooling cycle, as indicated by regions (4),(5) and (6) in FIG. 2, and as seen, during region (3) the refrigerator is effectively off.
The above defrost scheme is disadvantageous in that the defrost cycle is only initiated by the interruption and consequent termination of a cooling cycle. This results in a high energy consumption by the refrigerator along with the degradation of food stored within the refrigerator. In particular, the refrigerator consumes a large amount of energy since the compressor must not only lower the temperature of the storage compartment to below a prescribed temperature, but must now additionally compensate for the further rise in compartment temperature which is attributable to the defrosting cycle. Thus, the further rise in the compartment temperature along with the longer time period required by the compressor to lower the compartment temperature, gives rise the degradation of food which may be stored within a storage compartment of the refrigerator.
Furthermore, it has been found that there are a greater number of cooling cycles, and cooling cycles of longer duration, required during times of high ambient temperatures and high door opening activity, (e.g., dinner time during a hot humid day in August) and less cooling cycles during lower ambient temperatures and low door opening activity, (e.g., 3 a.m. in the morning). Therefore, the existing defrost scheme utilized by refrigerators tends to drive initiation of a defrost cycle toward the power utility's peak load period. Additionally, more cooling cycles and cycles of long duration are required during brown outs or immediately following a power outage, and therefore, a high probability of a defrost cycle being initiated exists at those times. Thus, there is no relationship of initiation of the defrost cycle as to the amount of frost on the evaporator coils, since the defrost cycle is not altered based on how much ice is melted, and the initiation time of the defrost cycle is unrelated to the needs of the power utility company.
A typical example of the above method is disclosed in U.S. Pat. No. 4,528,821 to Tershak et al. wherein the defrost cycle is executed while the operation of the cooling cycle is switched from the "on" state to the "off" state or during a period when the temperature within the refrigerator is at the upper end of its range at which foods deteriorate.
A still further type of defrost control is disclosed in U.S. Pat. No. 4,251,988 to Allard et al. This defrost control is referred to as an "adaptive" defrost control since it establishes the time between succeeding defrosting cycles as a function of the length of time that the defrost heater was energized during the first defrosting cycle. Another type of adaptive defrost control is disclosed in U.S. Pat. No. 4,481,785 to Tershak et al. This adaptive defrost control varies the length of an interval between defrosting cycles in accordance with the number and duration of compartment door openings, the duration of a previous defrosting cycle as corrected by the temperature of the evaporator coils prior to a defrost cycle and the length of time the compressor has been energized. However, the decrementing of the number and duration of refrigerator door openings does not result in an entirely accurate representation of the amount of frost which has formed on the evaporator coils due to the moisture introduced into the refrigerator while the refrigerator door is open. Accordingly, this results in a less-than-optimal defrost interval.
Thus, a common disadvantage with prior defrost systems is that they do not initiate a defrost cycle during an optimal time period according to the energy efficiency of the refrigerator, the peak demand loading needs of power utility companies and the degradation of food caused by a defrosting cycle being initiated during a warm ambient temperature period.
Furthermore, the above mentioned adaptive defrost controls are unable to be readily adapted for retrofit into existing refrigerator control systems. Rather, the control circuitry of refrigerators must be designed and configured for the implementation of such adaptive defrost controls.
Accordingly, there exists a need to provide a defrost system that will conserve energy and prevent the degradation of food by initiating a defrost cycle during an optimal time period which is most energy efficient after the completion of a cooling cycle.
It is an object of the present invention to initiate a defrosting cycle in a refrigerator during an off-peak demand period of utility companies which is most energy efficient for the refrigerator while also preventing the degradation of food stored within the refrigerator.
Further, there exists a need to provide a defrost control system that is configured to be readily adapted into existing refrigerators while being simple and inexpensive to manufacture.